1. Field of the Invention
The present invention relates to a catadioptric optical system that is suitably used for magnifying a sample (an object) to be observed, and relates to an image pickup apparatus having the catadioptric optical system.
2. Description of the Related Art
In a current pathological examination, a pathological sample (a sample) is directly observed by the human eye using an optical microscope. Recently, a so-called virtual microscope that obtains an image of the pathological sample as image data to be observed on a display is used. In the virtual microscope, since the image data of the pathological sample can be observed on the display, a plurality of users can observe the data at the same time. In addition, there are many advantages in that for example the image data can be shared with a distant pathologist to be examined when this virtual microscope is used. However, this method has a problem that it takes time in order to taking the image of the pathological sample to be obtained as the image data.
One of reasons for taking time is that the pathological sample in a wide shooting area has to be obtained as image data using a narrow shooting area of the microscope. When the shooting area of the microscope is narrow, one image is obtained by taking a plurality of images or scanning images to connect them. In order to reduce the number of times of taking the images compared to a conventional microscope to shorten the time for obtaining the image data, an optical system (an image pickup optical system) that has a wide shooting area is required.
Additionally, an optical system that has a wide shooting area and that has a high resolution in a visible range (in a wide wavelength range) is required in observing the pathological sample. The optical system having the high resolution is required not only in the usage of the pathological examination but also in a variety of fields.
Japanese Examined Application Publication No. S60-034737 discloses an objective lens of a microscope that includes a catadioptric optical system and that appropriately reduces an aberration in whole of a visible light range, which is suitable for the observation of a living cell or the like.
Japanese Unexamined Application Publication (Translation of PCT Application) No. 2007-514179 discloses an ultra-wideband ultraviolet microscope video system that uses a catadioptric optical system and that has a high resolution in a broad ultraviolet wavelength range to examine a defect existing on an integrated circuit or a photo mask.
PCT international publication No. WO00/039623 discloses a catadioptric optical system that exposes a fine pattern in a broad area and that is suitable for manufacturing a semiconductor device.
The objective lens of the microscope that is disclosed in Japanese Examined Application Publication No. S60-034737 appropriately reduces various kinds of aberrations in whole of the visible light range, but the size of the observation area is not necessarily sufficient. A catadioptric imaging system of the wideband microscope that is disclosed in Japanese Unexamined Application Publication (Translation of PCT Application) No. 2007-514179 appropriately reduces the aberration over the wide wavelength range and has a high resolution, but the size of the visible area is not necessarily sufficient.
The catadioptric imaging optical system disclosed in PCT international publication No. WO00/039623 has a high resolution over a wide area, but the width of the wavelength range in which the aberration has been appropriately corrected is not necessarily sufficient. A microscope lens for magnifying and observing the sample requires a large observation area and a high optical performance in a wide wavelength range.